Replacement of various joints is becoming increasing common due to a longer life expectancy leading to the likelihood of greater wear and tear and damage to our joints. Particularly, hip and knee replacement surgeries are increasing dramatically in the over 65 cohort of the population.
In all cases, it is critically important to not only replace a bony portion with a correctly sized prosthesis but it is also vital for patient comfort and to prevent further complications to achieve the correct orientation of a prosthetic component. A successful knee arthroplasty will largely depend upon the proper alignment of the prosthetic components. For example, abnormal valgus or varus alignment has been reported as a cause of implant loosening. Further, incorrect femoral rotational alignment may be a major cause of patella-femoral complications, tibio-femoral instability and early failure.
To achieve an optimal alignment of a prosthesis such as a femoral prosthetic component, surgeons reference certain landmarks on the bone. For achieving the correct rotational alignment of the femoral component, the anterior cut of the femur must be correct and this is often achieved by referencing one or more of the posterior condylar axis, the anterior-posterior axis (also known as Whiteside's line which involves the identification of one anterior point and one posterior point in the trochlea groove to produce an axis) or the Sulcus Line (which is a version of the anterio-posterior axis which involves the identification of multiple points along the trochlea groove and thereby allows for orientation along the coronal axis of the trochlea groove) and the trans-epicondylar axis (TEA) which a line running from the medial and epicondylar sulcus and the lateral epicondyle.
It has been shown that aligning the femoral component with the TEA optimises patella-femoral tracking and approximates the flexion-extension axis of the knee. However, in practice, it is often difficult to accurately identify the TEA and one option is to identify and mark the Sulcus line which is taken to be perpendicular to the TEA.
Several problems have been encountered in accurately marking the Sulcus line, however and the variance is substantial depending upon the landmarks selected and the angle at which the line is viewed. Additional error is produced by current techniques which translate the vertical Sulcus line into a horizontal line drawn across the femoral condyles for alignment of the cutting blocks. This geometrical error is accentuated when the femoral condylar surface is not perpendicular to the coronal axis of the Sulcus Line.
There is a need, therefore, to address the deficiencies of the prior art and provide a means to accurately utilise the Sulcus line to allow a surgeon to accurately position a prosthetic knee component for optimal rotational alignment.